OptiFine
By default, Minecraft is limited to rendering blocks at 16 pixels by 16 pixels. This mod adds support for HD textures; 32, 128, 256, even 512 pixels per block. It also adds a lot of options for better looks and better performance. Doubling your FPS (frames per second) is quite common. We recommend the OptiFine HD A4 Smooth for Minecraft 1.1 '(extends the Standard edition and removes lag spikes)' Features *FPS boost (examples) - doubling the FPS is common - decreases lag spikes and smooths gameplay *Support for HD Textures (info, examples) - HD textures and HD fonts (MCPatcher not needed) - custom terrain and item textures - animated terrain and item textures - custom HD Font character widths - custom colors - custom block color palettes - unlimited texture size *Configurable Smooth Lighting (examples) - from 1% - smooth lighting without shadows - to 100% - smooth lighting with full shadows *Performance: VSync Synchronizes framerate with monitor refresh rate to remove split frames and smooth gameplay *Smart Advanced OpenGL - more efficient, less artifacts - Fast - faster, some artifacts still visible - Fancy - slower, avoids visual artifacts *Fog control - Fog: Fancy, Fast, OFF - Fog start: Near, Far *Mipmaps (examples) Visual effect which makes distant objects look better by smoothing the texture details - Mipmap level - OFF, 1, 2, 3, Max - Mipmap type - Nearest, Linear Check the OptiFine AA edition for even better texture smoothing with Antialiasing and Anisotropic Filtering. *Better Grass Fixes grass blocks side texture to match surrounding grass terrain *Better Snow (examples, credit) Fixes transparent blocks textures to match surrounding snow terrain *Clear Water (examples) Clear, transparent water with good visibility underwater *Random Mobs Use random mob textures if available in the texture pack *Far View Increases view distance 3x. *FPS control - Smooth FPS - stabilizes FPS by flushing the graphics driver buffers (examples) - Smooth Input - fixes stuck keys, slow input and sound lag by setting correct thread priorities *Chunk Loading Control - Load Far - loads the world chunks at distance Far, allows fast render distance switching - Preloaded Chunks - defines an area in which no new chunks will be loaded - Chunk Updates per Frame - allows for faster world loading - Dynamic Updates - loads more chunks per frame when the player is standing still *Configurable Details - Clouds - Default, Fast, Fancy - Cloud Height - from 0% to 100% - Trees - Default, Fast, Fancy - Grass - Default, Fast, Fancy - Water - Default, Fast, Fancy - Rain and Snow - Default, Fast, Fancy - Sky - ON, OFF - Stars - ON, OFF - Depth Fog - ON, OFF - Weather - ON, OFF *Configurable animations - Water Animated - OFF, Dynamic, ON - Lava Animated - OFF, Dynamic, ON - Fire Animated - OFF, ON - Portal Animated - OFF, ON - Redstone Animated - OFF, ON - Explosion Animated - OFF, ON - Flame Animated - OFF, ON - Smoke Animated - OFF, ON - Void Particles - OFF, ON - Water Particles - OFF, ON - Rain Splash - OFF, ON - Portal Particles - OFF, ON - Dripping Water/Lava - OFF, ON - Terrain Animated - OFF, ON - Items Animated - OFF, ON *Fast Texturepack Switching Switch the current Texturepack without leaving the world *Fullscreen Resolution Configurable fullscreen resolution *Debug - Fast Debug Info - removes lagometer from debug screen - Debug Profiler - removes profiler from debug screen *Time Control Default, Day Only or Night Only - works in only in Creative mode *Autosave - Configurable Autosave interval - A fix for the famous Lag Spike of Death Video Tutorial